Vapor Locking

[West Peterson]

I am finding the need to install an electric fuel pump on my 1940 180. While I appreciate the "Seagraves" method versus installing in "series", I'm wondering if that is a little overkill for the manner in which I plan to use it...

Cold starts where the car has sat for more than a week, and...

on the occasional occasions when it starts to vapor lock.

In both instances, I'd use it for just a few seconds.

Any thoughts?

[Guest Randy Berger]

I don't like the "series" method. If your regular fuel pump has a torn diaphragm you could be pumping gas into your crankcase. I would rather run the electric fuel line beyond the normal pump and tee it in there. I would seriously consider placing a check valve there also.

[Packard enthus.]

Let's first remember WHAT vapor lock is, and WHERE it occurs. In the old days I often marveled at the guys who put clothes pins on the fuel lines, cow-bells, or prayed to the Great Space Monkey.

Vapor lock does not and CAN NOT occur between the fuel pump and the carb. For the simple reason that when gasoline is under pressure, it will not turn to a vapor.

Vapor lock occurs when the pressure on the fuel is REDUCED. Such as when you SUCK it from a tank by a fuel pump.

It gets HOT under a car on a hot day, especially on that portion of the fuel line BEFORE the fuel gets to the fuel pump. THAT is where vapor lock occurs. Cow bells, clothes pins, and praying to the Great Space Monkey only SEEM to help coincidentally. Keep the fuel line COLD on a hot day (not practical)...or pressurizing the fuel from the tank foward, is the simple solution.

Also, modern fuels have a lower "Ried Vapor Pressure" than gasoline avail. prior to the 2nd World War. Thus today's gasoline is much more prone to vapor lock. I have NO explanation why some pre-war - even some 50's cars NEVER seem to get vapor lock, others do at the drop of a hat. Wierd.

Simple solution...PRESSURIZE THE FUEL AT OR NEAR THE FUEL TANK. There are still several vendors selling 6 volt electric fuel pumps. I got so tired of vapor lock, and of the risk of a diaphragm failure, I simply removed the diaphragm pump from my car ( a Packard V-12) and run off the electric. (actually, in my installation, I have TWO in paralell, in case 1) one goes bad...and/or/.....2) someone in a Cadillac V-16 needs to be taught a lesson on a long uphill high speed grade....!).

Yes - I agree...there is a REMOTE risk of a diaphgram failure. But there is a greater risk of getting rear-ended if your car vapor-locks.

I say - go for a SIMPLE "series" installation - with your new electric fuel pump mounted as LOW and as CLOSE to the gasoline tank as possible.

[West Peterson]

That is exactly what I was thinking, but wanted to find out if anyone else is doing that. My normal pump is new (or rebuilt), so I'm not too concerned of the diaphgram failing. Also, my car does not have any "heat sheilds." But, knowing that modern gas vaporizes faster, I was thinking my time would be better spent installing an electric fuel pump than a heat shield (which may not solve anything).

[6219_Rules]

West, allow me to add that to keep the car looking original in the engine compartment, keep the fuel pump on, as long as the pump is in good condition (if not, fix it), and install the electric back low and by the tank as instructed by our dear senior member of the CCCA with the V-12.

I had a 1956 Cadillac with an original electric pump with a big glowing button. It solved my last vapor locking issue.

[West Peterson]

Yes. I'll keep the correct pump on the car, as I plan on using it 99.9% of the time. Thanks.

[mrpushbutton]

Put a cup of diesel fuel in your full tank of 87 octane pump regular. It will knock down the volatility of your newspeak gas to about what they had in 1940, and greatly reduce "vapor locking". I like Petey's idea about putting the pump back by the tank, that's how we did it but put a pressure regulator so that you can knock down the high(er) pressure of the electric to the 6-8 lbs. of your OE pump.

[Guest bkazmer]

I'm very willing to learn, but have you tried this diesel fuel trick - it adds low volatility fuel but doesn't remove the high volatility fraction. Vapor lock only requires a small portion of the fuel to boil.

[mrpushbutton]

A friend who works as a fuel compatibility engineer for Ford, who is also into old cars swears by it, with some scientific reasoning (you'll have to ask him).

My cars are form the 50's -60's I don't have this problem.

I worked with a very experienced antique car mechanic who insisted that vapor lock was a myth, an old wives tale. He insisted that what people were experiencing was (OE mechanical) fuel pump heat distortion that was breaking the prime of the pump. He was rather emphatic about getting a modern diaphragm, made from material that didn't mind today's gasoline, having two relatively flat halves to fasten together, then carefully cross-torquing the halves together so as to not distort the halves. Every car in the fleet we took care of that got his treatment ran beautifully, and never gave the slightest fuel delivery problems, including grueling tests like the 1999 Packard centennial parade in Warren. Shoot, we even had flat head V-8 Fords (the most notorious "vapor lockers" of them all!) that ran fine, no electric pump.

[West Peterson]

I agree that if everything is working "properly" (with the help of modern materials) vapor lock wouldn't happen. But I'm not sure i'd go so far as to say it's a myth.

[Owen_Dyneto]

You said your car has no heat shields, and there is part of your problem as it should have two of them, one mounting on the carburetor to shield it from the exhaust manifold, and the other around the fuel pump to direct cooling air from the fan. Buy these heat shields and try that first. Also one poster said your problem had to be int he fuel line from the tank because that was not under pressure. Well I agree with that, but the fuel in your carburetor is not under pressure either -- do you have the thick insulating block between the carb and the manifold in place? Personally, and I'm probably in the minority on this, I don't like electric fuel pumps unless absolutely necessary. First I've seen too many nice cars have underhood fires, and secondly when my engine has sat for a few weeks, I don't want it to start instantly, I want it to crank for a short time to distribute the oil to the cylinder walls and crank journals.

[carbking]

"Vapor lock is a myth"??? <img src="http://forums.aaca.org/images/graemlins/shocked.gif" alt="" />

Making a statement such as the above, simply because one has never experienced vapor lock, is like me saying that hurricanes never exist! Well, I have never seen one in Missouri!!! <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" />

Vapor lock most certainly does exist, normally inside the fuel pump, as that is where the largest concentration of heat (from the engine) contacts the fuel. While the fuel pump will still pump vapor, the effiency is greater reduced, and the supply to the carburetor is then interrupted.

Vapor lock may also occur, although less common due to pressure, in the fuel line between the fuel pump and the carburetor, if the fuel line is too close to the exhaust system. Vapor lock of this type will virtually only occur during idle conditions, when fuel demand is extremely low. Vapor lock under this condition will normally not cause stalling, unless the vapor condition spreads back to the fuel pump. As long as the fuel in the pump does not vaporize, the pump will eventually push the vapor through the carburetor. Vapor lock of this type will manifest itself as a very unstable idle, as the fuel level in the bowl will vary with incoming liquid/vapor. Use of an electric pump may not help this type of vapor lock.

Modern fuels are much more susceptible to vapor lock than gasoline from the 1960's and before.

Generally, the best defense against vapor lock is a "vapor return line", which would "T" from the main fuel line at the fuel pump or, better but obviously not original, at the carburetor. The vapor return line should be smaller than the fuel line, and goes back to and dumps into the fuel tank. As the vapor return line is smaller, there is more resistance to fuel flow, and the carburetor would then have first "dibs" on the fuel. Fuel not needed by the carburetor is shunted back to the tank; thus allowing the fuel pump to continue pumping.

This "fix" has the added benefit of maintaining a lower temperature of fuel delivered to the carburetor. Cooler fuel means marginally more power and fuel economy. The rule of thumb is that a 10 degree F. reduction in fuel temperature in the carburetor bowl is good for 1 percent increase in power and economy.

Electric pumps (my opinion) are fine if properly installed. This means wiring the pump with some safety device (normally an oil pressure switch); and either removing the original fuel pump completely, or leaving the original pump in place, but removing the "guts" and pipe the fuel internally straight through the pump. Electric pumps are "pusher" pumps, not suction pumps; and as such, must be mounted near the fuel tank for good results.

The biggest problem with electric pumps is the failure of the installer to understand pressures. ALL carburetors have design maximum pressure. MOST carburetors produced before circa 1955 have design pressures of LESS than 5 pounds, with a majority having a maximum of less than 4 pounds. Original gravity feed systems will generally have less than 1 pound. Too much pressure at the carburetor and fuel goes everywhere.

One other comment: a couple of posters have mentioned adding diesel to the fuel. "Skinned Knuckles" magazine did some testing on this issue a few years ago. I forget the exact percentage added; but knocking and pre-ignition was encountered prior to any noticable reduction in volatility. These were tests conducted by engineers specifically to determine if any benefit would occur. And while I do not have the equipment to scientifically duplicate this testing, experience gives me the exact same results. Again, others may have differing opinions. If it works for you, do it.

Jon.

[John_Marsh]

This may be nothing. In 1937 the Packard Six had flat panels at the base of the engine on either side to create a sort of wind tunnel. If these are missing air will disapate, causing the area by the fuel pump and carb to get warmer then it was designed for. My 1937 six is missing the passenger side piece, nor does it have any heat shields over the fuel pump and it did not over heat in the parade in 1999 in Warren. A former 1953 with those heat shields did give me a taste of vapor lock. Whether real or not.

[Guest sndtubes]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mrpushbutton</div><div class="ubbcode-body">A friend who works as a fuel compatibility engineer for Ford, who is also into old cars swears by it, with some scientific reasoning (you'll have to ask him).

My cars are form the 50's -60's I don't have this problem.

I worked with a very experienced antique car mechanic who insisted that vapor lock was a myth, an old wives tale. He insisted that what people were experiencing was (OE mechanical) fuel pump heat distortion that was breaking the prime of the pump. He was rather emphatic about getting a modern diaphragm, made from material that didn't mind today's gasoline, having two relatively flat halves to fasten together, then carefully cross-torquing the halves together so as to not distort the halves. Every car in the fleet we took care of that got his treatment ran beautifully, and never gave the slightest fuel delivery problems, including grueling tests like the 1999 Packard centennial parade in Warren. Shoot, we even had flat head V-8 Fords (the most notorious "vapor lockers" of them all!) that ran fine, no electric pump. </div></div>

Ihave a 1930 Buick (yeah I know, boo, I can't afford a Packard!) and am now experiencing vapor lock in the 90 degree plus heat. I will tell you that "The Old Carb Doc", Jeff Driebus, rebuilt the fuel pump in my car and specifically told me he used a "nitrile diaphram" which was supposed to stand up to today's fuel. So, at least in my case, the diaphram material did not help.

[Guest imported_PackardV8]

Thank you CarbKing for verifying that vapour lock CAN and does occur on the pressure side of the pump and even in the carb bowl itself and is usualy due to somekind of excessive heat introduction from engine malfunction or poor maintneance procedures.

I recently bought a Mr. Gasket Electric fuel pump to carry as a spare in my 56 Packard with WCFB. I bought the 5-7 pound version of the pump. Should i have bought the 4-5 pound version instead???? I've not tried to connect it to the car yet. I only need it as a spare for road side emergency.

[Guest imported_PackardV8]

What most people think is a vapour lock condition is almost always someother problem. Quite often rubber (actualy neoprene) hoses that are more than 5 to 7 years old. I've seen at least 2 situations where a weatherd and aged and cracked hose would suck air but not show significant signs of gas leakage. The cracks in the hose were not visible until the hose was removed and inspected.

Lots of older vehicles out there running around with rubber hose replacing steel lines. Severe internal rusting of steel lines. Other issues not related to vapour lock. plugged bowl vents. plugged gas cap vent. Exhaust leaks blowing on fuel lines. pin holes in fuel lines at a high point (going over top of rear axle that do not leak enuf gas to be evident but allow for significant air draught.

Some people claim issues with REGIONAL fuel compounding: I live in Tennessee and if ANY palce in the US should have fuel quality issues IT"S HERE. The "old gas" excuse: PRoven wrong by me too many times. I've started engines using gas that i KNOW had sat in the tank for as long as 3 years and MANY MANY times had sat in the tank for 9 months.

Fuel delivery problems are mechanical and maintenace in nature and RARELY if ever chemical in nature.

[Guest imported_PackardV8]

By the way, i tested my MR. Gasket Electric fuel pump (5-7 pound version). It will draw a steady a STEADY full stream of gasloine THREE FEET verticle (STREIGHT UP) using 1/4 id inch hose. Altho the instructions indicate the "push rather than pull efficiencey " advantage i can see no reason for it other than so-called vapour lock 'protection'.

Over the years and on at least 3 different occasions i can recall I've ran an older SW electric fuel pump mounted on the front fender well in emergency conditions quite often in HOT weather for as much as 400 miles or more at 70 mph with no problem until i could the factory pump replaced.

So, WHAT'S with this "push instead of pull" thing about Elec. pumps???? Vapour lock is NOT a reason. Is there some other reason????

[tbirdman]

OK so do I now have a fuel pump problem? I had the mechanical fuel pump on my 32 rebuilt. Car ran fine for over a week just using the rebuilt mechanical fuel pump, with roughly 200 miles put on the car. I had never used the electric fuel pump until the first time I strated the car after the winter project. Sunday I stopped for gas and a few miles after I leave the station, the car starts sputtering. Switching on the electric fuel pump solved the problem. In an attempt to fix the problem I drained the gas and added fresh gas from a different station thinking possible bad gas. I added STP gas treatment. I replaced the fuel filter in the line after the electric fuel pump. No change...car runs for about 5 miles and then starts sputtering and switching on the elctric fuel pump solves it.

Last night I replaced the elctric fuel pump with a new stewart wagner punp as the AC pump would not shut off once pressurized. I did not run the car after the installation, but verified that the pump shut off when pressurized. Also I noticed that the Sw was much louder than the AC it replaced. Tonight I plan to install a fuel pressure regulator to limit the pressure to 3 PSI.

Am I overlooking something? The outside and engine temperature has been relatively the same when it was working vs when the problem occurred.

[Ron Green]

A common problem with GM engines is the cam lobe wears down and the mechanical fuel pump lever doesn't have enough movement which then limits the fuel, starving the engine especially under load. Installing and using an electric fuel pump typically solves this problem until the cam can be replaced. Unsure of a Packard engine mechanicals however possibly this could be your problem?

[Packard enthus.]

BASICS OF VAPOR LOCK

I know..I know...why bother - we go thru this nonsence on about 5 month cycles in here - people who have "belief systems", and lack a basic education in the physical sciences, dont want to hear technical facts but DO want to sound important, keep giving other car enthusiasts nonsensical info.

I am opposed to the above practice - we need to HELP our fellow car buffs with LEGIT. info. to keep them in the hobby.

Over the years, the "vapor pressure" of gasoline has risen. For the simple reason is, the eaiser it is to get the liquid gasoline into a vapor, the better the car runs. The introduction of high pressure fuel delivery systems ( most fuel injected cars now have high pressure fuel pumps mounted in the gas tank ) has enabled the industry to enjoy a MUCH higher Ried vapor pressure than would have been possible in the old days.

Gasoline vapor pressure was so low in the early days, that, if you wanted to get a car running on a cold morning, you either heated it by towing it inside, or had a neat gadget that some luxury cars had, called a "Fuelizer", which was nothing more than an additional spark plug in the intake manifold, to help TRY and get the burning process going.

As fuel vapor pressures have risen, vehicles with the old style diaphragm "suction" type pumps are experiencing more and more "boiling off" of gasoline. Vapor lock, or the "boiling off" of gasoline can be eliminated by putting the gasoline under pressure. Very simple solution - mount an electric fuel pump as close to the gas tank as possible, and as low as possible.

If the gasoline is under pressure, it cant vapor lock. Physical impossibility. Yes, I know about the cow magnets, prayers to Buddah, and rubbing one's belly three times in the right direction.

Yes, we all got our cars with ordinary diaphragm/suction type fuel pumps going, for many years. But that was then. Gasoline has changed. On a hot day, your car's structure gets warm. Your gasoline line runs all the way from the gas tank to your engine-driven fuel pump. It is under SUCTION until it gets into your engine-driven diaphram fuel pump. THAT is where it is going to boil. Basic physical laws - folks, you reduce the ambient pressure, and you increase the chances of the liquid becoming a vapor. Our diaphram type fuel pumps cannot pump a vapor.

So - bottom line, no matter how well you "restore" your vehicle, including its old style fuel pump, you cant get 1950's gasoline ! Install an electric fuel pump PROPERLY, and say good bye to vapor lock.

[Ron Green]

Quote; "I am opposed to the above practice - we need to HELP our fellow car buffs with LEGIT. info. to keep them in the hobby"

I am unsure as to what you are getting at however if it is in regards to using a electric fuel pump I too don't recommend it. Tbirdman's problem could very easily be non vapor-lock related from what he is describing. I simply pointed out a common problem with the fuel pump leaver that gets overlooked many times when diagnosing a fuel problem.

[tbirdman]

6686L,

I understand your post, but still question why the car ran fine for a week and under the same operating conditions is now not with no changes to the system. If I took out the car today when the temp is close to 100 and the car exhibited the problem, I could see that the temp may have contributed to the problem. But the problem started to occur when operating conditions were pretty much stable from one time to another.

[Guest AntarcticDave]

I had a recent experience on my 47 Cadillac. It seemed like vapor lock symptoms, but turned out to be something else. A friend suggested isolating possible trouble areas. I have an electric auxillary pump located low near the fuel tank. First I disconnected the line from the tank and ran the car from a gas can - same problem. Next I bypassed the line from the tank to the auxillary - same problem. Next I bypassed the fixed line from the auxillary to the mechanical pump. The problem went away (well, still get some bubbles in really hot conditions, but not nearly as many). I ended up replacing the fixed line. Apparently there was a crack or pinhole somwehere in it, or the connection to the flex line, that was opening up when it got hot, letting the mechanical pump suck in air. The electric pump solved the issue at lower temperatures by pressuring that line. It only showed up hot when the leak became more sustantial. Just thought I'd throw that out, another thing to look at. I know I was hitting my head against the wall for awhile with my car.

Dave

[Guest imported_PackardV8]

Peter. Your argument, UNlike an insurance policy, does NOT hold gasoline. It's tantamount to arguing wheather to use a 12 pound sledge hammer as opposed to using an 8 pounder to kill a fly on a plate glass window.

TRUE, gas formulations HAVE changed over the last 20 - 30 years. But the specifics u site are not significant to create a fear of vapour lock provided the car is mechanicaly sound.

[Packard enthus.]

I dont fear vapor lock. I dont get vapor lock. The reason I dont get vapor lock, is because I have TWO electric fuel pumps, in parallel, both mounted LOW, so that my fuel lines are under pressure pretty much thru-out the length of the car. ( Packard Twelves are BIG engines that CAN, when "pushed" under extreme conditions (as in when going up a long steep grade at obscene speeds), suck more gas than one ordinary electric fuel pump can deliver ).

You are WRONG WRONG WRONG about fuel formulation per Reid Vapor pressure. It IS much higher these days, and that is why MANY cars with carbuerators fed by engine driven vacuum style fuel pumps DO vapor lock.

I have no answer why SOME cars with engine-driven diaphragm fuel pumps do not vapor lock even with today's fuels. The monster (just a hair under 800 cu. in) V-12 in my American La France did not vapor lock even coming up the Needles Grade in August ( I-40 between Needles and Barstow). I drove it to New York and back one summer, and never even turned on the electric fuel pump I installed because I thought I might need it.

Other car buff friends of mine DO have vapor lock problems, and I KNOW there is nothing wrong with their cars.

[6219_Rules]

Each and every time I have had a problem running my car, whether the 1947 or the 56, at altitude in the summer, it was fixed by an electric pump mounted low back by the tank. My cars are not beautifully restored Cadillacs. They are drivers with old and aging parts that are replaced when I can afford it, or when the breakdown forces me to replace it.

New fuel lines are a must just as new brake lines are for the proper operation of the car. However, just my experience with old aspirated engines is that when they buck and studder, or refuse to restart, an electric pump solves the problem.

Ah for a new Rochester four barrel on the '56! That would be loverly.

[imported_v12lincoln]

an easy fix to vapor lock can be as easy as changing your fuel filter and adding a return line to the filler neck. I learned this from my 70 440 six pack challenger. I was using a regular fuel filter when I rebuilt my engine which was fine till temps got up around 100 and stuck in rush hour traffic here in calif. I looked through the shop manual and found these engines and the Hemis used a vapor recovery fuel filter, about $56 through year one, then I found the same thing from Fram that they used on the early 60s 421 SD pontiacs. they have to be mounted straight up but work great. you just have to make a return line to your tank, I go through the filler neck because its easy to get to. The filter has two outlets one inlet, one outlet goes to the carb the outher goes back to the tank, with an electric fuel pump it will recycle the fuel so it never gets hot, its cheap and easy and if you still have the heat shield over your pump it can be hidden never to be seen.

[Joe Block]

West

John Urich in San francisco make several heat shield for super -8 too

Joe

[West Peterson]

Thanks, Joe

I have a heat shield, I just need to install it. Also, I just noticed that my plastic inline gas filter is leaning on the engine block. I'm sure that isn't of much help in trying to keep the gas cooler. I just had my gas tank out of the car and it was perfectly clean inside, so I think I'll remove the filter altogether.